Deep inside the Lascaux cave, past the world-renowned Great Hall of the Bulls, where Paleolithic artists painted a colorful menagerie of horses, deer, and bulls, starts a lesser-known corridor known as the Apse. There, at the bottom of a sixteen-foot pit, next to fine drawings of a wounded bison and a rhinoceros, lies one of the rare depictions of a human being in prehistoric art. The man is lying flat on his back, palms up and arms extended. Next to him stands a bird perched on a stick. Nearby lies a broken spear that was probably used to disembowel the bison, whose intestines are hanging out.

The person is clearly a man, for his penis is fully erect. And this, according to the sleep researcher Michel Jouvet, illuminates the drawing’s meaning: it depicts a dreamer and his dream. As Jouvet and his team discovered, dreaming occurs primarily during a specific phase of sleep, which they dubbed “paradoxical” because it does not look like sleep; during this period, the brain is almost as active as it is in wakefulness, and the eyes ceaselessly move around. In males, this phase is invariably accompanied by a strong erection (even when the dream is devoid of sexual content). Although this weird physiological fact became known to science only in the twentieth century, Jouvet wittily remarks that our ancestors could easily have noticed it. And the bird seems the most natural metaphor for the dreamer’s soul: during dreams, the mind flies to distant places and ancient times, free as a sparrow.

This idea might seem fanciful were it not for the remarkable recurrence of imagery of sleep birds, souls, and erections in the art and symbolism of all sorts of cultures. …

… that humans use, and now you can too! (Continued from the previous post.)

3) Recursion. What if you have one mirror facing a second mirror, so the first mirror shows what’s in the second mirror, which shows what’s in the first mirror …? What if you take a chameleon, which tries to take on the color of its surroundings, and put it on a mirror? What if you point a video camera at the very screen that’s showing what the video camera is pointing at? What if (getting mathematical) you use a function in defining that same function? What if you use the cleaning attachment from your vacuum cleaner to suck dust off the vacuum cleaner itself? (Okay, the last one is a bit lame.) The basic idea in each of these cases is called recursion, which is a major concept in mathematics and computer science. Douglas Hofstadter’s Gödel, Escher, Bach is all about recursion. Some people think recursion – nesting ideas about ideas inside one another in a potentially infinite hierarchy, or (for syntax) phrases inside phrases — is central to human uniqueness. Noam Chomsky has lately been pushing a hard-core version of this argument. Here he is with Robert Berwick defending his view.

Related to the idea of recursion is the idea of “meta-representation”: not just having ideas about the world but having ideas about ideas, being able to put a box around a proposition, and then attaching a tag to it that says the equivalent of “This is true” or “This is false” or “This will be true later” or “Suppose this were true,” and then manipulating it accordingly. A nice little essay in “imagination,” elaborating this idea, is here from Simon Baron-Cohen, best known as an authority on autism.

4) Shared intentionality. Suppose you and I are friends with a couple, Fred and Wendy Smith. I tell you “I saw Wendy Smith kissing a man in the park yesterday.” Logically speaking, there’s nothing to say the man wasn’t Fred. But you’ll probably assume that I meant she was kissing someone other than Fred. Why? Well if the man had been Fred I could just as easily have said “I saw Wendy Smith kissing Fred in the park yesterday.” Since I didn’t say that, you assume I mean to convey the man wasn’t Fred. Note this only works if both of us try to pack as much relevant information into our sentences as possible and know the other person is doing the same. (If you think this sounds like recursion, you’re right.) Back in the 1950s, Paul Grice, a philosopher, worked out a lot of how we pack non-literal meanings into sentences. But the same principles are at work even when people are communicating non-linguistically. This leads to another theory of human uniqueness: human beings are uniquely good at developing shared intentions with one another: each party knows the other party is trying to communicate something, so they converge on the correct answer. People may have been doing this even before language evolved. Following up on this can quickly get you into game theory, where a central concept is “common knowledge”: not just “I know X” and “You know X,” but “I know X,” and “I know X is common knowledge to us,” and similarly for you. The cc option on your email generates common knowledge: if you see someone’s address there then they see yours, and you know they know you know, etc. Here’s a philosophical treatment.

But you can skip the philosophy if you want and move on to a telling little piece of anatomy that’s relevant here. In most mammals, including chimpanzees, the sclera (white of the eyes) is not visible. It’s hard to tell where a chimpanzee is looking, easy for a human. Human eyes make it easy to cooperate in sharing attention, a first step in developing shared intentions. If you know your card games, chimpanzees are playing poker, humans are playing bridge.

Our discussion of human uniqueness on Logarithmic History has been frustratingly short on specific dates. But human sclera are probably a fairly simple trait genetically, and we may soon enough discover the genes involved and even tell how long ago they mutated.

There are people who think that human beings are nothing special. Sure (the argument goes) people have uniquely large brains. But all sorts of creatures have unique features. Elephants are the only animals with trunks. Tamarins and marmosets are the only primates that give birth to twins. Platypuses are the only venomous mammals. Spotted hyenas are the only mammals whose females sport pseudo-penises (through which they give birth!). And so on. If we could ask members of these species they’d claim that they’re the special ones.

But of course we can’t ask them, and in any case, this isn’t a very convincing argument. Human beings have an absolutely outsize impact on the Earth, and the advent of human beings looks like one of the major evolutionary transitions, comparable in importance to the origin of the eukaryotic cell or multicellular life. But even if we buy this, it still leaves open the question of whether there’s a key adaptation – a One Weird Trick – that accounts for the exceptional course of human evolution. Here are some candidates that being are being batted around these days:

1) The cognitive niche. The basic idea is at least as old as Aristotle, that human brings are defined by their capacity for Reason. A modern version of this is advocated by evolutionary psychologist John Tooby and cognitive scientist Steven Pinker. Pinker in particular has elaborated the argument that humans are uniquely adapted to acquire and share knowledge, by virtue of a suite of cognitive, social, and linguistic adaptations. We’ve already touched on several aspects of this: Human beings seem to have taken the capacity for thinking about physical space and retooled it for thinking about the abstract cognitive space of possession – a social relationship. (Other abstract cognitive spaces include kinship, time, and change-of-state.) And humans seem to harness the machinery for processing the sounds of interacting solid objects in creating major categories of phonemes. For a more complete exposition, here’s an academic article by Pinker, and a talk on youtube.

2) Culture. Rob Boyd and Pete Richerson, who’ve done a lot of mathematical modeling of cultural evolution, are skeptical about the “cognitive niche” argument. Too much culture, they argue, is things that have been learned by trial-and-error, and are passed on from one generation to the next without people understanding why they work. Boyd and Richerson appeal, as anthropologists have for generations, to the importance of culture. We mentioned earlier their argument that the frequency of climate change in the Ice Age was nicely calibrated to favor social learning rather than individual learning or instinct. Joseph Henrich provides a recent defense of the importance of culture. Contra Pinker, he thinks humans often don’t have a good cause-and-effect understanding of the things they do, but depend heavily on imitation and the accumulated wisdom of the elders. And see this post, for the importance of High Fidelity cultural transmission in the evolution of animal and human intelligence.

The first Archaeopteryx discovered, found in 1861, is the most famous fossil ever (barring maybe some close human relations). It came at the right time, providing dramatic evidence for the theory of evolution.

There may be psychological reasons why Archaeopteryx had the impact it did. Here’s my argument anyway:

According to Jorge Luis Borges, the following is a classification of animals found in a Chinese Encyclopedia, the Celestial Emporium of Benevolent Knowledge.

Those that belong to the Emperor

Embalmed ones

Those that are trained

Suckling pigs

Mermaids (or Sirens)

Fabulous ones

Stray dogs

Those that are included in this classification

Those that tremble as if they were mad

Innumerable ones

Those drawn with a very fine camel hair brush

Et cetera

Those that have just broken a flower vase

Those that, at a distance, resemble flies

Although some scholars have taken this list seriously (Hi, Michel Foucault!), there’s no evidence that this is anything but a Borgesian joke. Anthropologists have actually spent a lot of time investigating the principles underlying native categorizations of living things, and found they are not nearly as off-the-wall as Borges’ list. These categorizations obey some general principles, not quite the same as modern biologists follow, but not irrational either. (Naming Nature: The Clash Between Instinct and Science is good popular review of ethno-biology, the branch of anthropology that studies different cultures’ theories of biology and systems of classification Did you know there are specialized brain areas that handle animal taxonomy? Or try here for a scholarly treatment.)

At the highest level is usually a distinction between plants and animals. This doesn’t necessarily match the biologists’ distinction between Plantae and Animalia, but rather usually follows a distinction between things that don’t and do move under their own power. Even babies seem to make a big distinction between shapes on a screen that get passively knocked around, and shapes that move on their own. i.e. are animated.

Among larger animals (non-bugs/worms) the first large scale groups to receive a label of their own are almost always birds, fish, and snakes, in no particular order. These categories are telling: each represents a variety of locomotion (flying, swimming, slithering) other than the stereotypical mammalian walking/running. (Many folk classifications lump bats with birds and whales with fish, and they may also separate flightless birds like the cassowary from others.) So whether a creature moves on its own, and how it moves are central to folk categorizations of living kinds, even if not to modern scientific taxonomy. And so finding an animal that seems to be a missing link between two (psychologically) major domains of life — birds and terrestrial animals — is going to be a Big Deal, cognitively, upsetting people’s ideas that it takes God’s miraculous intervention to create animals that fly, or to condemn the Serpent to slither.

Deep inside the Lascaux cave, past the world-renowned Great Hall of the Bulls, where Paleolithic artists painted a colorful menagerie of horses, deer, and bulls, starts a lesser-known corridor known as the Apse. There, at the bottom of a sixteen-foot pit, next to fine drawings of a wounded bison and a rhinoceros, lies one of the rare depictions of a human being in prehistoric art. The man is lying flat on his back, palms up and arms extended. Next to him stands a bird perched on a stick. Nearby lies a broken spear that was probably used to disembowel the bison, whose intestines are hanging out.

The person is clearly a man, for his penis is fully erect. And this, according to the sleep researcher Michel Jouvet, illuminates the drawing’s meaning: it depicts a dreamer and his dream. As Jouvet and his team discovered, dreaming occurs primarily during a specific phase of sleep, which they dubbed “paradoxical” because it does not look like sleep; during this period, the brain is almost as active as it is in wakefulness, and the eyes ceaselessly move around. In males, this phase is invariably accompanied by a strong erection (even when the dream is devoid of sexual content). Although this weird physiological fact became known to science only in the twentieth century, Jouvet wittily remarks that our ancestors could easily have noticed it. And the bird seems the most natural metaphor for the dreamer’s soul: during dreams, the mind flies to distant places and ancient times, free as a sparrow.

This idea might seem fanciful were it not for the remarkable recurrence of imagery of sleep birds, souls, and erections in the art and symbolism of all sorts of cultures. …

The first Archaeopteryx discovered, found in 1861, is the most famous fossil ever (barring maybe some close human relations). It came at the right time, providing dramatic evidence for the theory of evolution.

There may be psychological reasons why Archaeopteryx had the impact it did. Here’s my argument anyway:

According to Jorge Luis Borges, the following is a classification of animals found in a Chinese Encyclopedia, the Celestial Emporium of Benevolent Knowledge.

Those that belong to the Emperor

Embalmed ones

Those that are trained

Suckling pigs

Mermaids (or Sirens)

Fabulous ones

Stray dogs

Those that are included in this classification

Those that tremble as if they were mad

Innumerable ones

Those drawn with a very fine camel hair brush

Et cetera

Those that have just broken a flower vase

Those that, at a distance, resemble flies

Although some scholars have taken this list seriously (Hi, Michel Foucault!), there’s no evidence that this is anything but a Borgesian joke. Anthropologists have actually spent a lot of time investigating the principles underlying native categorizations of living things, and found they are not nearly as off-the-wall as Borges’ list. These categorizations obey some general principles, not quite the same as modern biologists follow, but not irrational either. (Naming Nature: The Clash Between Instinct and Science is good popular review of ethno-biology, the branch of anthropology that studies different cultures’ theories of biology and systems of classification Did you know there are specialized brain areas that handle animal taxonomy? Or try here for a scholarly treatment.)

At the highest level is usually a distinction between plants and animals. This doesn’t necessarily match the biologists’ distinction between Plantae and Animalia, but rather usually follows a distinction between things that don’t and do move under their own power. Even babies seem to make a big distinction between shapes on a screen that get passively pushed around, and shapes that move on their own. i.e. are animated.

Among larger animals (non-bugs/worms) the first large scale groups to receive a label of their own are almost always birds, fish, and snakes, in no particular order. These categories are telling: each represents a variety of locomotion (flying, swimming, slithering) other than the stereotypical mammalian walking/running. (Many folk classifications lump bats with birds and whales with fish, and they may also separate flightless birds like the cassowary from others.) So whether a creature moves on its own, and how it moves are central to folk categorizations of living kinds, even if not to modern scientific taxonomy. And so finding an animal that seems to be a missing link between two (psychologically) major domains of life — birds and terrestrial animals — is going to be a Big Deal, cognitively, upsetting people’s ideas that it takes God’s miraculous intervention to create animals that fly, or to condemn the Serpent to slither.

Deep inside the Lascaux cave, past the world-renowned Great Hall of the Bulls, where Paleolithic artists painted a colorful menagerie of horses, deer, and bulls, starts a lesser-known corridor known as the Apse. There, at the bottom of a sixteen-foot pit, next to fine drawings of a wounded bison and a rhinoceros, lies one of the rare depictions of a human being in prehistoric art. The man is lying flat on his back, palms up and arms extended. Next to him stands a bird perched on a stick. Nearby lies a broken spear that was probably used to disembowel the bison, whose intestines are hanging out.

The person is clearly a man, for his penis is fully erect. And this, according to the sleep researcher Michel Jouvet, illuminates the drawing’s meaning: it depicts a dreamer and his dream. As Jouvet and his team discovered, dreaming occurs primarily during a specific phase of sleep, which they dubbed “paradoxical” because it does not look like sleep; during this period, the brain is almost as active as it is in wakefulness, and the eyes ceaselessly move around. In males, this phase is invariably accompanied by a strong erection (even when the dream is devoid of sexual content). Although this weird physiological fact became known to science only in the twentieth century, Jouvet wittily remarks that our ancestors could easily have noticed it. And the bird seems the most natural metaphor for the dreamer’s soul: during dreams, the mind flies to distant places and ancient times, free as a sparrow.

This idea might seem fanciful were it not for the remarkable recurrence of imagery of sleep birds, souls, and erections in the art and symbolism of all sorts of cultures. …